US Roaming Charges

I just returned from the US with a huge roaming bill. I had used data a couple of times to order Ubers so I was expecting some charges. Anyway I quickly received my €60 spend alert and at one stage I had to remove the cap out of desperation to order an Uber. When I checked my bill I had a number of the €30 per day charges for 50MB or whatever it is which is fine. But there is one "excess roaming charge" that appears for over €350. I have no idea what that is. I had accepted I'd be paying over €60 for the little bit of usage but didn't use data on my phone for much more than ordering a few Ubers. My bill is now nearly €500. Can anyone help?